I've now had three different hvac contractors out and they've made 3 different recommendations for addressing the cooling problem in my upstairs space.
I have what was a one-storey house built in 1930 which has been expanded by framing the attic space and adding a couple of dormers. Total upstairs space is 800-900 feet and is used for office, master suite and laundry room. House is located in Atlanta where it gets quite hot in summer. We have an 8 year old, 1.5 ton, 10 SEER Lennox unit which cannot keep the space cool. On an 85-95 degree day, inside temps never get below 83 degrees and that's with the system running all day. The unit has been checked and is functioning properly; it just can't keep up.
The three contractors have suggested 2.0 ton, 2.5 ton and 3 ton, 13 SEER units. One has also suggested swapping out the 15 year old gas furnace (which is functioning well) for a heat pump unit to save on gas bills. (My annual natural gas cost is $1200 total for both upstairs and downstairs systems, so I don't know whether this makes any sense.) The contractors suggesting 2.5 and 3 ton units have said they would need to add vents and returns. Here's what I have already:
3 @ 15" x 8
3 @ 12" x 8
1 @ 12" x 6
1 @ 15" x 16
1 @ 16" x 8
No one has performed a Manual J. The 2.5 and 3.5 ton guys have said that the roof adds so much heat that the usual square foot calculations don't apply, but that in their "experience" I need the sizing they suggest.
Seems like a lot of money to spend based on a couple of contractors' intuition. (However, both these contractors are well-known in the community and have been around for 20+ years.) Anyone have suggestion of what I should do?
When the attic space was converted,they may have added a lot or a little insulation to the walls and attic,window size and type effect size as well.
Call around untill you find a contractor that can and will do the the Man. J,and a Man. D to design the ducts.